The aim of the present study was to study the influence of several thermal processing methods such as cooking and drying on biologically active compounds of red pitaya. Flesh of red pitaya was subjected to five different thermal processes: oven cooking at 95ºC 30 min, oven cooking at 95ºC 60 min, oven cooking at 105ºC 60 min, drum drying, and spray drying. Total phenolic content, scavenging activity, antioxidant activity and dietary fiber contents of the fresh and processed red pitaya were subsequently determined. The effect of oven cooking on antioxidant parameters of red pitaya were highly significant compared to fresh one (p<0.05). Whereas, drum drying and spray drying were the best methods for antioxidant preservation in this fruit, compared to the other thermal processes applied in this study. Among all of the heating temperatures applied in this study, drum drying was the best method for preservation of total phenolic content, radical scavenging and antioxidant activity, and 95ºC for 30 min oven cooking was the best process to preserve dietary fiber parameters of this fruit.